1. Field of the Invention
The present invention relates to a process for producing a peptide in the presence of pepsin.
2. Description of Prior Art
Recently, various peptides having physiological activity have been disclosed, and development of techniques for synthesis of peptides has been ongoing. Typical processes for producing peptides include an azide method; a mixed acid anhydride method; a dicyclohexyl carbodiimide method; and an active ester method. However, in accordance with these conventional processes, various disadvantages occur, e.g., racemization, side reactions, necessarily complicated temperature control, long reaction times, etc. Especially in the fragment condensation method, unavoidable racemization is a particularly bothersome disadvantage. In actuality, in any synthesis of peptides, the racemization problem is serious. When racemization occurs, the purity of the product is decreased and the separation of the impure isomer is necessitated. This is a severe disadvantage in an industrial operation.
In addition to the organic chemical processes, certain peptide synthes using the enzyme papain have been disclosed. (See, for example, O. K. Behrens and M. Bergmann; J. Biol. Chem., 129,587 (1939) and H. B. Milne and Warren Kilday; J. Org. Chem., 30, 64 (1965). Thereby, the racemization problem has been solved. However, these methods are applicable only to preparations of di- or tri-peptides. When a tetra- or higher peptide is synthesized by using a papain having varying substrate specificity, several side reactions involving hydrolysis of a peptide occur, e.g., transpeptidation and formation of plastein. Consequently, this scheme cannot be used for industrial peptide synthesis.
It is known that proteolytic enzymes (protease) have the characteristic property of hydrolyzing peptides in good reproducible operation, and under mild conditions without bothersome side reactions. Accordingly, the proteolytic enzymes have been utilized for various studies of chemical structures of polypeptides and proteins. By using them, the preliminary structures of various natural polypeptides such as insulin have been determined. One typical such enzyme is pepsin, classified among the digestive enzymes of endopeptitases (enzymes which are active to an inner bond of peptide chains) as a proteolytic enzyme.
It would be most desirable to have a process for production of a peptide which is free from the above disadvantages.